Polymer-metal interfaces, interdiffusion

Although it might be argued that the penetration of polymer molecules into the pores of an anodized metal surface is a form of interfacial diffusion, the present text will not consider such a process to represent an example of the diffusion theory. However, it has been reported [53] that interdiffusion does occur across polymer/metal interfaces when certain metals are evaporated or sput-... 

In summary, the interdiffusion of polymer chains across a polymer/polymer interface requires the polymers (adhesive and substrate) to be mutually soluble and the macromolecules or chain segments to have sufficient mobility. These conditions are usually met in the autohesion of elastomers and in the solvent welding of compatible, amorphous plastics. In both these examples interdiffusion does appear to contribute significantly to the intrinsic adhesion. However, where the solubility parameters of the materials are not similar, or one polymer is highly crosslinked, crystalline or below its glass transition temperature, then interdiffusion is an unlikely mechanism of adhesion. In the case of polymer/metal interfaces it appears that interdiffusion can be induced and an interphase region created. But this effect enhances the interfacial adhesion by improving the adsorption of the polymeric material rather than by a classic diffusion mechanism. 

Rather little work has been reported on the use of conducting polymers in active semiconductor devices. A problem in organic pn-junctions is the interdiffusion of dopants destroying the abrupt interface. In Schottky junctions made of (the more stable) p-type polymers, metals with low work functions must be used. These metals, such as aluminium (work function 4 3 eV) are typically reactive and oxidize easily. 

In butt welding (also known as butt fusion and hot plate fusion), a heated metal plate is placed between the squared and cleaned ends of adjacent lengths of pipe. Slight pressure is applied to maintain good contact between the pipe ends and the plate. After a preset time the plate is rapidly withdrawn and the molten pipe ends are brought into contact with sufficient pressure to produce intimate contact and create interior and exterior circular beads of polymer. The pressure is then reduced and the joint is allowed to solidify. In smaller pipes (up to approximately 2 ft in diameter) this process can be automated, which produces more consistent joints than can be attained manually. Control variables include temperature, dwell time, initial contact pressure, and holding force during solidification. The application of too much pressure to the molten pipe ends will result in thin bonds that are weak. Conversely, with too little pressure the interdiffusion of molecules across the interface will not be adequate. 

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